Batteries :Charges can be separated by several means to produce
a voltage. A battery uses a chemical reaction to produce energy and
separate opposite sign charges onto its two terminals. As the charge is
drawn off by an external circuit, doing work and finally returning to
the opposite terminal, more chemicals in the battery react to restore
the charge difference and the voltage. The particular type of chemical
reaction used determines the voltage of the battery, but for most
commercial batteries the voltage is about 1.5 V per chemical section or
cell.

Batteries with higher voltages really contain
multiple cells inside connected together in series. Now you know
why there are 3 V, 6 V, 9 V, and 12 V batteries, but no 4 or 7 V
batteries. The current a battery can supply depends on the speed
of the chemical reaction supplying charge, which in turn often
depends on the physical size of the cell and the surface area of
the electrodes.

The size of a battery also limits the amount of chemical reactants
stored. During use, the chemical reactants are depleted and
eventually the voltage drops and the current stops.

Even with no current flow, the chemical reaction proceeds at a
very slow rate (and there is some internal current flow), so a
battery has a finite storage or shelf life, about a year or two in
most cases.

In
some types of batteries, like the ones we use for the robot, the
chemical reaction is reversible: applying an external voltage and
forcing a current through the battery, which requires work,
reverses the chemical reaction and restores most, but not all, the
chemical reactants. This cycle can be repeated many times.
Batteries are specified in terms of their terminal voltage, the
maximum current they can deliver, and the total current capacity
in ampere-hours.

You should handle batteries carefully, especially the ones we use in
this course. Chemicals are a very efficient and compact way of
storing energy. Just consider the power of gasoline or explosives,
or the fact that you can play soccer for several hours powered only
by a slice of cold pizza for breakfast. Never connect the terminals
of a battery together with a wire or other good conductor. The
battery we use for the RoboBoard is similar to the battery in cars,
which uses lead and sulphuric acid as reactants. Such batteries can
deliver very large currents through a short circuit, hundreds of
amperes. The large current will heat the wire
and possibly burn you; the resulting rapid internal chemical
reactions also produce heat and the battery can explode, spreading
nasty, reactive chemicals about. Charging these batteries with too
large a current can have the same effect. Double check the circuit
and instructions before connecting a battery to any circuit.

Learn More on Electronics:

Rules of Electrical
Circuits: * A voltage of 1V across a resistance
of 1 Ohm will cause a current flow of 1 Amp, and the resistor will
dissipate 1 Watt (all as heat).

What
is an electronic circuit? A circuit is a structure that directs
and controls electric currents, presumably to perform some useful
function. The very name "circuit" implies that the structure is
closed, something like a loop.

Current: Charge is mobile and can flow freely in certain
materials, called conductors. Metals and a few other elements and
compounds are conductors. Materials that charge cannot flow through
are called insulators. And then there are some materials called
semiconductors, that seemed to be good conductors sometimes but much
less so other times. Silicon and germanium are two such materials.
The flow of charge is called electrical current. Current is measured
in amperes (a), amps for short.

Voltage:
Voltage is something is a type of "pressure" that drives electrical
charges through a circuit.
Bodies with opposite
charges attract, they exert a force on each other pulling them
together. The magnitude of the force is proportional to the product
of the charge on each mass.

What is charge?
Charge
may be defined as the quantity of unbalanced electricity in a body
(either positive or negative) and construed as an excess or
deficiency of electrons. Charge comes in two forms,
positive (+) , and negative charge ( - ) .

Resistors: A Resistor isan electrical device that resists the flow of
electrical current. It is a passive device used to
control, or impede the flow of, electric current in an
electric circuit by providing resistance, thereby developing
a drop in voltage across the device.
The value of a resistor is measured in ohms
and represented by the Greek letter capital omega. Resistors usually
have a brown cylindrical body with a wire lead on each end, and
colored bands that indicate the value of the resistor.

Ohm’s Law: Ohm's law describes the relationship between
voltage, V , which is trying to force charge to flow, resistance, R
, which is resisting that flow, and the actual resulting current I .

Capacitors: In simple words, we can say that a capacitor is a device
used to store and release electricity, usually as the result
of a chemical action. Also referred to as a storage cell, a
secondary cell, a condenser or an accumulator. A Leyden Jar
was an early example of a capacitor.

Inductors:
An inductor isan electrical device (typically a
conducting coil) that introduces inductance into a circuit.
An inductor is a passive electrical component designed to
provide inductance in a circuit. It is basically a coil of
wire wrapped around an iron core. simplest form an inductor
is made up of a coil of wire. The inductance measured in
henrys, is proportional to the number of turns of wire, the
wire loop diameter and the material or core the wire is
wound around.

Semiconductor devices: A conductor made with semiconducting
material. Semiconductors are made up of a substance with electrical
properties intermediate between a good conductor and a good
insulator. A semiconductor device conducts electricity poorly at
room temperature, but has increasing conductivity at higher
temperatures. Metalloids are usually good semiconductors.

Silicon: Silicon, atomic number 14 on the periodic table, is a semiconducting
material from which integrated circuits (computer chips of all
types--processors, memory chips, etc.; CCDs; transistors; etc.) are
created.

Silicon is one of the most common elements. Silicon is also the
semiconductor material out of which almost all modern transistors are
made.

Diodes:
A Diode is an electronic device that allows
current to flow in one direction only. It is a semiconductor that consists of a p-n junction. They are used
most commonly to convert AC to DC, because they pass the
positive part of the wave, and block the negative part of
the AC signal, or, if they are reversed, they pass only the
negative part and not the positive part.